Re: [Intel-gfx] [RFC PATCH 1/4] drm/i915: Drop user contexts on driver remove

[Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>]

Hi Tvrtko,

On Thu, 2020-05-28 at 11:14 +0100, Tvrtko Ursulin wrote:
> On 18/05/2020 19:17, Janusz Krzysztofik wrote:
> > Contexts associated with open device file descriptors together with
> > their assigned address spaces are now closed on device file close.  On
> 
> i915_gem_driver_remove looks like module unload to me, not device file 
> close. So..

Not only module unload ...

> 
> > address space closure its associated DMA mappings are revoked.  If the
> > device is removed while being open, subsequent attempts to revoke
> > those mappings while closing the device file descriptor may may be
> > judged by intel-iommu code as a bug and result in kernel panic.
> > 
> > Since user contexts become useless after the device is no longer
> > available, drop them on device removal.
> > 
> > <4> [36.900985] ------------[ cut here ]------------
> > <2> [36.901005] kernel BUG at drivers/iommu/intel-iommu.c:3717!
> > <4> [36.901105] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
> > <4> [36.901117] CPU: 0 PID: 39 Comm: kworker/u8:1 Tainted: G     U  W         5.7.0-rc5-CI-CI_DRM_8485+ #1
> > <4> [36.901133] Hardware name: Intel Corporation Elkhart Lake Embedded Platform/ElkhartLake LPDDR4x T3 CRB, BIOS EHLSFWI1.R00.1484.A00.1911290833 11/29/2019
> > <4> [36.901250] Workqueue: i915 __i915_vm_release [i915]
> > <4> [36.901264] RIP: 0010:intel_unmap+0x1f5/0x230
> > <4> [36.901274] Code: 01 e8 9f bc a9 ff 85 c0 74 09 80 3d df 60 09 01 00 74 19 65 ff 0d 13 12 97 7e 0f 85 fc fe ff ff e8 82 b0 95 ff e9 f2 fe ff ff <0f> 0b e8 d4 bd a9 ff 85 c0 75 de 48 c7 c2 10 84 2c 82 be 54 00 00
> > <4> [36.901302] RSP: 0018:ffffc900001ebdc0 EFLAGS: 00010246
> > <4> [36.901313] RAX: 0000000000000000 RBX: ffff8882561dd000 RCX: 0000000000000000
> > <4> [36.901324] RDX: 0000000000001000 RSI: 00000000ffd9c000 RDI: ffff888274c94000
> > <4> [36.901336] RBP: ffff888274c940b0 R08: 0000000000000000 R09: 0000000000000001
> > <4> [36.901348] R10: 000000000a25d812 R11: 00000000112af2d4 R12: ffff888252c70200
> > <4> [36.901360] R13: 00000000ffd9c000 R14: 0000000000001000 R15: ffff8882561dd010
> > <4> [36.901372] FS:  0000000000000000(0000) GS:ffff888278000000(0000) knlGS:0000000000000000
> > <4> [36.901386] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > <4> [36.901396] CR2: 00007f06def54950 CR3: 0000000255844000 CR4: 0000000000340ef0
> > <4> [36.901408] Call Trace:
> > <4> [36.901418]  ? process_one_work+0x1de/0x600
> > <4> [36.901494]  cleanup_page_dma+0x37/0x70 [i915]
> > <4> [36.901573]  free_pd+0x9/0x20 [i915]
> > <4> [36.901644]  gen8_ppgtt_cleanup+0x59/0xc0 [i915]
> > <4> [36.901721]  __i915_vm_release+0x14/0x30 [i915]
> > <4> [36.901733]  process_one_work+0x268/0x600
> > <4> [36.901744]  ? __schedule+0x307/0x8d0
> > <4> [36.901756]  worker_thread+0x37/0x380
> > <4> [36.901766]  ? process_one_work+0x600/0x600
> > <4> [36.901775]  kthread+0x140/0x160
> > <4> [36.901783]  ? kthread_park+0x80/0x80
> > <4> [36.901792]  ret_from_fork+0x24/0x50
> > <4> [36.901804] Modules linked in: mei_hdcp i915 x86_pkg_temp_thermal coretemp crct10dif_pclmul crc32_pclmul ghash_clmulni_intel ax88179_178a usbnet mii mei_me mei prime_numbers intel_lpss_pci
> > <4> [36.901857] ---[ end trace 52d1b4d81f8d1ea7 ]---
> > 
> > Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/gem/i915_gem_context.c | 38 +++++++++++++++++++++
> >   drivers/gpu/drm/i915/gem/i915_gem_context.h |  1 +
> >   drivers/gpu/drm/i915/i915_gem.c             |  2 ++
> >   3 files changed, 41 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > index 900ea8b7fc8f..0096a69fbfd3 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> > @@ -927,6 +927,44 @@ void i915_gem_driver_release__contexts(struct drm_i915_private *i915)
> >   	rcu_barrier(); /* and flush the left over RCU frees */
> >   }
> >   
> > +void i915_gem_driver_remove__contexts(struct drm_i915_private *i915)
> > +{
> > +	struct i915_gem_context *ctx, *cn;
> > +
> > +	list_for_each_entry_safe(ctx, cn, &i915->gem.contexts.list, link) {
> > +		struct drm_i915_file_private *file_priv = ctx->file_priv;
> > +		struct i915_gem_context *entry;
> > +		unsigned long int id;
> > +
> > +		if (i915_gem_context_is_closed(ctx) || IS_ERR(file_priv))
> > +			continue;
> > +
> > +		xa_for_each(&file_priv->context_xa, id, entry) {
> 
> ... how is driver unload possible with open drm file descriptors, or 
> active contexts? 

... but also PCI driver unbind or PCI device remove, with the module
still loaded.  That may perfectly happen even if a device file
descriptor is still kept open.

> If something is going wrong sounds like something else.

I think we might consider that "something" as intel-iommu code, but see
also the last paragraph of my response below.

> 
> drm postclose -> i915_gem_context_close -> closes all contexts and puts 
> all vm. What can remain dangling? An active context? But there is idling 
> via i915_gem_driver_remove -> i915_gem_suspend_late.

Idling doesn't release DMA mappings which may then be released as late
as on i915_gem_driver_release.  If that doesn't happen on device remove
only later on last device close, intel-iommu triggers a bug.

I reported that issue to intel-iommu maintainers several months ago[1].
They even agreed that was something that might need to be fixed[2], I
provided them with information how the issue could be reproduced
easily[3] but no progress has been reported since then.  If you think
the issue should be definitely fixed on intel-iommu side, please help
me to convince intel-iommu maintainers to take care of that.

However, please note DMA-API also complains about DMA mappings still
left active when device is removed.  That may indicate we should rather
fix that on our side.

Thanks,
Janusz

[1] https://marc.info/?l=linux-kernel&m=156689857510234&w=2
[2] https://marc.info/?l=linux-kernel&m=156706978013967&w=2
[3] https://marc.info/?l=linux-kernel&m=156749651025416&w=2

> 
> Regards,
> 
> Tvrtko
> 
> > +			struct i915_address_space *vm;
> > +			unsigned long int idx;
> > +
> > +			if (entry != ctx)
> > +				continue;
> > +
> > +			xa_erase(&file_priv->context_xa, id);
> > +
> > +			if (id)
> > +				break;
> > +
> > +			xa_for_each(&file_priv->vm_xa, idx, vm) {
> > +				xa_erase(&file_priv->vm_xa, idx);
> > +				i915_vm_put(vm);
> > +			}
> > +
> > +			break;
> > +		}
> > +
> > +		context_close(ctx);
> > +	}
> > +
> > +	i915_gem_driver_release__contexts(i915);
> > +}
> > +
> >   static int gem_context_register(struct i915_gem_context *ctx,
> >   				struct drm_i915_file_private *fpriv,
> >   				u32 *id)
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.h b/drivers/gpu/drm/i915/gem/i915_gem_context.h
> > index 3702b2fb27ab..62808bea9239 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_context.h
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.h
> > @@ -110,6 +110,7 @@ i915_gem_context_clear_user_engines(struct i915_gem_context *ctx)
> >   
> >   /* i915_gem_context.c */
> >   void i915_gem_init__contexts(struct drm_i915_private *i915);
> > +void i915_gem_driver_remove__contexts(struct drm_i915_private *i915);
> >   void i915_gem_driver_release__contexts(struct drm_i915_private *i915);
> >   
> >   int i915_gem_context_open(struct drm_i915_private *i915,
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index 0cbcb9f54e7d..87d3c4f5b6c6 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -1189,6 +1189,8 @@ void i915_gem_driver_remove(struct drm_i915_private *dev_priv)
> >   	/* Flush any outstanding unpin_work. */
> >   	i915_gem_drain_workqueue(dev_priv);
> >   
> > +	i915_gem_driver_remove__contexts(dev_priv);
> > +
> >   	i915_gem_drain_freed_objects(dev_priv);
> >   }
> >   
> > 

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